1. Field of the Invention
The present invention relates to a liquid crystal display device (LCD) and a method for manufacturing the same, and more particularly, to a method for improving adhesion between an organic layer and a pixel electrode of an LCD.
2. Discussion of the Related Art
Generally, a conventional liquid crystal display device includes two panels with a liquid crystal layer between them. A first panel (an active panel) of the LCD includes switching elements such as thin film transistors (TFTs) and pixel electrodes. A second panel (a color filter panel) of the LCD includes color filters and common electrodes.
Referring to FIGS. 1A and 1B, a conventional LCD having a reversed stagger type thin film transistor (TFT) and a method for manufacturing the same will be described.
As shown in FIG. 1A, a gate electrode 60 is formed on a transparent substrate 10. A gate insulation layer 50 is formed on the transparent substrate 10 covering the gate electrode 60. A semiconductor layer 90 is formed on the gate insulation layer 50 over the gate electrode 60. First and second doped semiconductor layers 92a and 92b are formed on the semiconductor layer 90 in separate regions. A source electrode 70a is formed on the first doped semiconductor layer 92a in ohmic contact with the semiconductor layer 92a. A data line 70 connected to the source electrode 70a is formed on the gate insulation layer 50. A drain electrode 70b is in ohmic contact with the second doped semiconductor layer 92b. Therefore, a switching element of the LCD (i.e., the TFT), is formed on the transparent substrate 10. An organic protection layer 55 including benzo-cyclo-butene is deposited on the transparent substrate 10 and the TFT. A contact hole 30a is formed in the organic protection layer 30 in order to expose a portion of the drain electrode 70b. A pixel electrode 40 is formed on the organic protection layer 30. The pixel electrode 40 is connected to the drain electrode 70b through the contact hole 30a.
The organic protection layer 55 is used because the surface of the organic protection layer 55 is planar after being coated onto an uneven surface of the transparent substrate 10 and the TFT, and because the organic protection layer 55 has a lower dielectric constant than an inorganic material. Therefore, the pixel electrode 40 can be made larger, overlapping the data line 70. Thus, an organic material is used as a protection layer for an LCD having a high aperture ratio. A photo-resist pattern 88 for patterning the pixel electrode 40 is extended until it overlaps a portion of the data line 70, as shown in FIG. 1A.
When the pixel electrode 40 is formed by etching an indium tin oxide (ITO) layer using photo-lithography, an edge of the ITO layer can be attacked by an etchant, because vacancies result from weak adhesion between the ITO layer and the organic protection layer. Therefore, the etchant attacks the vacancies, and the pixel electrode 40 is over-etched. FIG. 1B shows etching results after the pixel electrode 40 is formed using the conventional method. Element A in FIG. 1B shows a peeled portion of the pixel electrode and elements B and C show over-etched portions of the pixel electrode 40.